[FFmpeg-devel] [PATCH] Matroska demuxer adds WebVTT support

Nicolas George nicolas.george at normalesup.org
Fri Jul 19 12:33:36 CEST 2013

Le decadi 30 messidor, an CCXXI, Matthew Heaney a écrit :
> Just so I'm understanding, I think the change you asking me to make
> involves some or all of the following steps:
> (1) change the existing webvtt demuxer to output packets that match their
> embedded representation in WebM.


> (2) change this Matroska demuxer patch to push webvtt frames downstream, as
> is, in their embedded form.

Yes. Unless I am mistaken, it would make the patch trivial.

(That is a general principle IMHO: adding support for codec X in format Y
should only require adding the map between the codec id for X and whatever
identifier used in Y; see commit 66aabd7 for example. If it requires more,
then there is something wrong somewhere, but not necessarily under ffmpeg's

> (3) add a WebVTT codec that understands webvtt frames as embedded in a WebM
> file, and converts them to some canonical text track format

I suspect WebVTT is recent and confidential enough, and we can dispense with
the "add new / deprecate old" routine and directly change the packet format.

> (4) change the existing webm muxer to accept a new packet format

Yes. I am very sorry I missed the discussion at this time, or I would have
said the same thing, and it may have avoided redundant work.

> (5) change the existing webvtt muxer to accept a new packet format


Of course, other can disagree with me, this is open to discussion.

> I'm on vacation for a couple of weeks, so this work will have to wait until
> I return.

No problem.

> No,  Just *.vtt and *.webm.

That is very good news. I just hope that if someone adds support for WebVTT
in another generic format, they will have the intelligence of using the same
format as Matroska. Otherwise, one of the demuxers will need a special case;
that is what I had in mind when I spoke of "not necessarily under ffmpeg's
control" above.

> No account log-in should be necessary.

They asked me for it when I tried to download the file. Google's requirement
of an account or not is a mystery to me.

> I'm on vacation, so I don't have access to my work computer, but you can
> simply extract the text track from the file, as ffmpeg has a webvtt muxer
> now.

I would rather have a pair of corresponding authoritative files instead of
producing one myself, but I will try to do without. Thanks.


  Nicolas George
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 198 bytes
Desc: Digital signature
URL: <http://ffmpeg.org/pipermail/ffmpeg-devel/attachments/20130719/b8b5973c/attachment.asc>

More information about the ffmpeg-devel mailing list